The protocol is designed to evaluate children with more extensive disease or systemic mastocytosis and to better understand those children that do not resolve their disease or progression of systemic mastocytosis. Classification of their disease will augment their current management and more clearly define the prognosis. The protocol also follows children with cutaneous disease from prior LAD protocols and families with more than one affected child to identify possible markers of progression. All patients are currently stable and have not had any adverse events. A total of 41 subjects were accrued since protocol approval with all variants of pediatric-onset mastocytosis: urticaria pigmentosa, diffuse cutaneous mastocytosis, mastocytoma, and indolent systemic mastocytosis. The information we are collecting from subjects enrolled in the protocol provides much needed information for the community at large. This protocol will help to identify factors that may be associated with disease that does not resolve. Moreover, in those children with indolent systemic mastocytosis, this protocol will identify prognostic markers for disease progression into adulthood.